PlanetMinis Forums banner
1 - 18 of 18 Posts

·
Registered
Joined
·
45 Posts
Discussion Starter · #1 ·
I put a TB 140 in my Gpx. I also used the Crower g2 cam. I used good pump fuel riding it today. The thing quit during the second moto.The crown was cracked aslost exactly to the shape of the ring land.:cry: Has this happened to anyone else? Do I need to be using race gas? I also damaged the exhaust valve. WOuld it be worth it to rebuild and got to a big valve head? One lobe on the cam was a bit scored too, is this an issue with these cams?
 

·
Registered
Joined
·
5,831 Posts
I ran that same exact setup for many hours with no issues. Ran fine on high test pump gas. Were you getting good oil flow to the head. Sounds as though you cooked it and maybe starved the top end of oil.
 

·
Registered
Joined
·
45 Posts
Discussion Starter · #3 ·
Nope, there is no scoring whatsoever.The crown cracked due to detonation as far as I can tell. The oiling wasn't an issue on my 125. I heard it ping a couple of times. I guess it was worse than I thought.:(
 

·
Registered
Joined
·
3,516 Posts
What octane were you using? Also, was it jetted correctly? If it was too lean then it would have gotten pretty hot. The hotter the engine gets the more apt it is to detonate especially if jetting is off or high enough octane fuel is not used.
 

·
Registered
Joined
·
3,516 Posts
Well, all I can say is it sounds like you ran it lean as all. That would cause the engine to get really hot and detonate. And if the cam lobe was scored then that could be a sign of a lack of oil but even if it isn't it stills sounds like you ran it lean. That's really all I can tell you. You can ask for second opinions but I am pretty sure that is what has happened.

Many and I mean many people have ran the 140 and 146 kits w/ no problems. The main thing you have to do w/ any big bore kits, cams, exhausts, and carbs is you have to rejet when something is done. And you can't guess at it. It can't be done in just a few minutes either. It takes time to do it correctly. Always run it rich when you first break it in. What carb were you running and what jets were in it and what's your elevation or where are you located?
 

·
Vendor
Joined
·
10,568 Posts
hows the plug look ??



the tb kit is kinda high comp and race gas may be needed



the bvh will lower the comp and give better flow



we do also have a 1mm base gasket



and if its really a 140 i have a few pistons i can discount



let me know what you need
 

·
Registered
Joined
·
45 Posts
Discussion Starter · #15 ·
The plug is tan, not grey or white. The score in the cam may have been on initial startup or perhaps some piston debris got through there. The piston did break apart a bit. I asked about jetting it when I purchased the kit and was told it was rich to start with so I would be fine. Stock pitster carb. We are at 700 ft the temp was around 80, high humidity.. hard packed track. Is the Crower g2 a bit much for this application? My buddy has the same setup with a TB cam.. his bike rips. Could I punch it out ang go to a 146 now that I damaged it? What is req'd piston to cylinder clearance? Thanks to all for your input.:)
 

·
Registered
Joined
·
45 Posts
Discussion Starter · #17 ·
dougtrip said:
way to close on compression. you are running the stock gpx head you need to run race gas to be safe.
I am running the stock head. I compared it to another Lifan head. The intake tract on mine is twice the diameter??? I understand the compression ratio could be in the 12:1 range. I don't know what the timing is but race gas is almost certainly req'd or at least mixed with pump gas. That's my thinking anyway.
 
1 - 18 of 18 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top